I just tried installing AC 4.0 on Windows Home Server(I have one runnint at home) and it works wonderful.
I would recommend that if you dont want domain headaches and active dir etc, then I feel Windows Home Server(WHS) is the best option. It will give you the following benefits
1) implement RAID for you
2) act as file server
3) act as AC server
4) will backup all your vista/win 7 clients (nightly).
I am so big a fan of nightly backup that WHS does. It has saved me 2 times with almost perfect restore.
